What is un IR

Hi,
I do not understand what is un IR.
Can someone explain it ?
Thanks

“Simply put, an impulse response (IR) is an audio file that contains a capture of the inherent sonic characteristics of a piece of gear, acoustic environment, or playback system”. Check here: https://support.roland.com/hc/en-us/articles/13368801407771-What-is-an-Impulse-Response-or-IR-